Ferromagnetic particles include iron oxide type fine particles which are conventionally used and ferromagnetic metal particles which have recently been used to improve magnetic recording density as well as a reproduction output due to its high saturation magnetization and high coercive force as described in, for example, U.S. Pat. Nos. 4,054,530, 4,061,824 and 4,352,859.
Research and studies have been conducted on magnetic recording tape (a so-called "metal tape") prepared by using ferromagnetic metal particles to put the product into practical use for video recording, because a metal tape has higher recording density than a conventionally used iron oxide type recording tape. A system wherein a compact video tape recorder which uses a metal tape and which is associated with a video camera has been proposed. In comparison with the VHS system or the Beta system which have recently been used, this system is designed to have a higher recording density more than twice, about 1/2 the diameter of the head cylinder and about 1/2 the relative speed between the head and the tape. Accordingly, the recording wavelength in this system is half that of the VHS or Beta system and is assumed to have a wavelength of 1.mu. or less (about 0.6.mu.).
This system must provide an image quality the same as or higher than that of the VHS system and the Beta system in recording and reproducing under those conditions. Therefore, if the image quality of this system is evaluated under the same conditions as that of the VHS system or the Beta system, a CN ratio (that is, the ratio of the output of reproduced signals/modulation noise on recording the FM carrying wave) of +6 dB or more higher than that of the VHS system of Beta system is required.
Various conditions must be met for the magnetic recording medium to have the above-described requirements, and naturally problems have occurred.
As the recording wavelength becomes shorter, the coercive force (Hc) of the tape must be increased to some extent. The surface of the magnetic recording layer must be made as smooth as possible to minimize spacing loss between the magnetic head and the magnetic recording layer.
The dispersibility of the ferromagnetic particles must be increased and a calendering treatment must be completely carried out to make the surface of the magnetic recording layer smooth. These are also effective to decrease noise. Further, it is very effective and important to decrease the particle size of the ferromagnetic particles.
However, if the particle size is decreased, the following problems arise. That is, the durability of a magnetic recording layer is decreased, head clogging easily occurs in a short period of time during use of the still image mode of the VTR, output is insufficient, and the surface of a magnetic recording layer is scraped away by the magnetic head.
Additionally, the thickness of the magnetic recording tape must be decreased as the video tape recorder becomes more compact, whereby curling easily occurs and the magnetic recording tape cannot therefore intimately contact the magnetic head. Thus satisfactory recording cannot be carried out.